1. Field of the Invention
This invention relates generally to medical devices and, more particularly, to methods, apparatus, and systems using an improved electrode for providing electrical signal therapy to a target body tissue of a patient.
2. Description of the Related Art
A variety of electrical or neural activity constantly occurs throughout the human body. For example, the central nervous system (CNS) is generally a hub of electrical or neural activity requiring appropriate coordination. The brain supervises the central nervous system (CNS). Properly controlled electrical or neural activity enables the brain to coordinate various mental and body functions to maintain homeostasis.
In addition to a drug regimen or surgical intervention, potential treatments for many diseases and disorders include implantation of a medical device in a patient for providing electrical signal therapy to body tissue, which may be referred to as “electrical stimulation.” In particular, by selectively applying therapeutic electrical signals to one or more electrodes coupled to the patient's neural tissue, an implantable medical device (IMD) may electrically stimulate a target tissue location. This device may be used to sense or treat a patient's physiologic parameter, disease, condition or disorder. (The word “or” is used herein in the inclusive sense, i.e., “and/or” or “A, B, or both,” unless a particular instance of it is expressly indicated to be in the exclusive sense).
Therapeutic electrical signals have been used to apply an electrical signal to a variety of neural structures of the body, including, more particularly, cranial nerves such as the vagus nerve. To provide vagus nerve stimulation to a patient, a neurostimulator device may be implanted in a target location in the patient's body. Such a neurostimulator device system may comprise an electrical signal generator, attached to an electrical lead having one or more electrodes coupled to the vagus nerve. For example, a method of providing electrical neurostimulation therapy to a patient may comprise applying a stimulus to an electrode coupled to a branch or a main trunk of a selected cranial nerve of the patient.
The signal may be used to induce afferent action potentials on the nerve and thereby increase the flow of neural signals up the nerve, toward the brain. The signal may also (or alternatively) generate efferent action potentials to modulate a neural response in one or more body structures of the patient, such as any of the numerous organs innervated by efferent signals on the vagus nerve. Finally, therapeutic electrical signals may also or additionally be used to inhibit neural activity or to block neural impulses from moving up or down the nerve the nerve. As used herein, the terms “stimulate” and “modulate” are interchangeable and refer to delivery of a signal (which may comprise an electrical, magnetic, or chemical stimulus) to a target body area, regardless of whether its effects include generation of afferent action potentials, generation of efferent action potentials, or the blocking of endogenous action potentials. Therapeutic electrical stimulation of the vagus nerve has been used to treat epilepsy and depression.
More generally, the endogenous electrical activity (i.e., activity attributable to the natural functioning of the patient's own body) of a neural structure of a patient may be modulated in a variety of ways. In particular, the electrical activity may be modulated by exogenously applied (i.e., from a source other than the patient's own body) electrical, chemical, or mechanical signals applied to the neural structure. The modulation (hereinafter referred to generally as “neurostimulation” or “neuromodulation”) may involve the induction of afferent action potentials, efferent action potentials, or both, in the neural structure, and may also involve blocking or interrupting the transmission of endogenous electrical activity traveling along the nerve. Electrical neurostimulation or modulation of a neural structure refers to the application of an exogenous electrical signal (as opposed to a magnetic, chemical or mechanical signal), to the neural structure. Electrical neurostimulation may be provided by implanting an electrical device underneath the skin of a patient and delivering an electrical signal to a nerve such as a cranial nerve. The electrical neurostimulation may involve performing a detection, with the electrical signal being delivered in response to a detected physiologic parameter. This type of stimulation is generally referred to as “active,” “feedback,” “closed loop,” or “triggered” stimulation. Alternatively, the system may operate without a detection system once the patient has been diagnosed with epilepsy (or another medical condition), and may periodically apply a series of electrical pulses to the nerve (e.g., a cranial nerve such as a vagus nerve) intermittently throughout the day, or over another predetermined time interval. This type of stimulation is generally referred to as “passive,” “non-feedback,” “open loop,” or “prophylactic,” stimulation. The stimulation may be applied by an implantable medical device that is implanted within the patient's body.
Many types of electrodes have been developed to facilitate electrical signal therapy for a target neural structure. For example, circumneural electrodes surround a portion of a nerve longitudinally to provide electrical stimulation of the nerve. The electrical stimulation may modulate electrical signals or impulses carried by the nerve. Alternatively or additionally, an electrode may sense electrical signals carried by the nerve. For example, a medical device, such as an implantable medical device may use such an electrode to stimulate or sense nerve activity on a portion of a tissue.